I'm interested in the Amerind language this name came from and the derivation of its meaning "three".

In association with the Shasta tribe of California or Mt. Shasta (their traditional home area), the consensus seems to be that the meaning is unknown. It's apparently not a word in Shastan or the surrounding tribal languages, and the tribe and its neignbors referred to itself/them by other names entirely.

If you can shed any light on the origin of "three" as a meaning, we'd be very interested.